This application incorporates by reference the disclosures of co-pending patent applications Ser. No. 09/651,688 by Masashi Takayanagi entitled xe2x80x9cFour-Cycle Outboard Motorxe2x80x9d and Ser. No. 09/650,829 by Keisuke Daikoku and Masashi Takayanagi entitled xe2x80x9cFour-Cycle Outboard Motorxe2x80x9d each of which is filed concurrently with the present application and is assigned to the assignee of the present application.
1. Field of the Invention
The present invention relates to an engine holder structure for a four-cycle outboard motor.
2. Description of the Related Art
Most outboard motors have a vertical-type engine which is mounted in the upper part of an engine holder attached to the hull via a clamp bracket and has a crankshaft disposed substantially vertically inside the engine. In the case of a four-cycle engine, an oil pan is generally disposed below the engine holder.
In some outboard motors, the drive shaft that transmits the drive force of the crankshaft to the propeller is disposed offset from the crankshaft. In outboard motor engines of this sort, only the cylinder block and the crankcase of the engine are fixed to the engine holder as shown in Japanese Laid-open Patent Application No. 2-274691, for example.
Also, as shown in Japanese Laid-open Patent Application Nos. 4-345592 and 10-218090, for example, an engine and an oil pan of a conventional outboard motor are securely fixed to an engine holder with separate bolts, and the bolts that securely fix the engine pass through the oil pan and engine holder from below whereby the engine holder and the oil pan are secured together with the cylinder block of the engine.
However, a structure wherein only the cylinder block and crankcase of the engine are fixed to the engine holder has a small interfacial area (or connection area) between the engine and engine holder which may result in the engine being attached with insufficient rigidity, especially in a large-scale outboard motor.
Also, since the cylinder head is not fixed to the engine holder, oil that has lubricated the interior of the cylinder head has to pass through the cylinder block before it can be guided to the oil pan, which may result in a more complex structure and weight increase.
Furthermore, in a structure where the engine and the oil pan are securely fixed to the engine holder with separate bolts, which pass through the oil pan and the engine holder from below whereby the engine holder and the oil pan are secured together with the cylinder block of the engine, the assembly rigidity of the entire outboard motor is low and many bolts are also required so that an increased number of components and an increased amount of labor are required for assembly.
With the foregoing in view, it is an object of the present invention to provide an engine holder structure for a four-cycle outboard motor wherein the attachment rigidity of the engine can be increased with a simple structure.
The present invention satisfies the above-described needs by providing an engine holder structure for a four-cycle outboard motor where an engine principally composed of a crankcase, a cylinder block and a cylinder head is mounted above an engine holder, where an oil pan is disposed therebelow, where a crankshaft is disposed substantially vertically inside the engine, and where the rotational force of this crankshaft is transmitted to a propulsion device via a drive shaft; wherein the engine holder structure is characterized in that the shaft center of the drive shaft is disposed offset from the shaft center of the crankshaft.
According to another aspect of the present invention, an engine holder structure for a four-cycle outboard motor comprises an engine principally composed of a crankcase, a cylinder block and a cylinder head that are mounted above an engine holder, an oil pan disposed therebelow, a crankshaft disposed substantially vertically inside the engine, wherein the rotation of this crankshaft is transmitted to a propulsion device via a drive shaft, wherein the engine holder structure is characterized in that the shaft center of the drive shaft is disposed offset from the shaft center of the crankshaft, and the cylinder head, the cylinder block and the crankcase are all securely fixed to the engine holder.
According to yet another aspect of the present invention, the engine holder and the oil pan may further be fastened together with at least one of the components of the engine.
Also, according to another aspect of the present invention, the engine holder and the oil pan may be fastened together with the cylinder block and the cylinder head.
Also, according to another aspect of the present invention, an oil drop hole may be formed in the lower surface of the cylinder head at the side of the interface between the cylinder head and the engine holder, and another oil drop hole may be formed in the upper surface of the engine holder at the side of the interface between the cylinder head and the engine holder.
Also, according to another aspect of the present invention, the shaft center of the drive shaft is disposed offset to the rear of the shaft center of the crankshaft.